packaging: setup: revert nfs config on cleanup

Revert /etc/sysconfig/nfs to its original contents on cleanup.

Added a function editConfigContent in util to generalize edit loops
that read conf files and do some changes to them. Used it to edit
/etc/sysconfig/nfs as well as /etc/httpd/conf.d/ssl.conf and
/var/lib/pgsql/data/postgresql.conf.

Bug-Url: https://bugzilla.redhat.com/1013347
Change-Id: I74dd4c1556bd6479fcf10f85fcbe083f215e0854
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
Signed-off-by: Yedidyah Bar David <didi@redhat.com>